This song plays as everyone starts to believe that Tweek and Craig are in a relationship, while the two lie in their beds confused about what is transpiring. A majority of this song is spent looking at Yaoi art of them.
The entire song is not heard in the episode, and the lyrics below is only the excerpt heard in the show.
The Book of Love is long and boring,
No one can lift the damn thing.
It's full of charts and facts and figures,
And instructions for dancing.
I love it when you read to me
You can read me anything.
The Book of Love has music in it.
In fact, that's where music comes from.
Some of it's just transcendental.
Some of it's just really dumb.
I love it when you sing to me
You can sing me anything.